thread compound

is heavy grease, or grease-like lubricant, used to facilitate assembly and disassembly of threaded connections; it lubricates, seals, prevents seizing and galling, and protects against rust and corrosion. Typical applications include oil well tubing, casing threads, and drill pipe joints; water, gas, steam, and drainage lines; nuts and bolts.

Also see anti-seize compound.

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